August 26, 2011

Research Confirm UK’s Atomic Clock To Be Most Accurate

Researchers have found that an atomic clock at the U.K.'s National Physical Laboratory (NPL) has the best long-term accuracy of any other clock in the world.

Studies of the clock's accuracy show it is nearly twice as accurate as previously thought.

The clock would lose or gain less than a second in about 138 million years.

The NPL's CsF2 clock is a "caesium foundation" atomic clock, in which the "ticking" is provided by the measurement of the energy required to change a property of caesium atoms known as "spin".

It is the electromagnetic waves that are required to accomplished this "spin flip" that are measured. Once 9,192,631,770 peaks and troughs of these waves go by, one standard second passes.

The clock has caesium atoms inside it that are gathered into bunches of 100 million or so and pass through a cavity where they are exposed to these electromagnetic waves.

The clock's frequency is adjusted until the spins are seen to flip, then the researchers know the waves are at the right frequency to define the second.

The clock provides an "atomic pendulum" that the world's clocks can be compared, ensuring they are all ticking at the same time.

Scientists measure the accuracy of caesium fountain clocks by evaluating the uncertainties of all the physical effects known to cause frequency shifts in the clock's operation, including atomic interactions with external fields, collisions between atoms, and the construction of the atomic clock's subsystems.

In 2010, the U.K.'s atomic clock was on par to be the best in accuracy at about one part in 2,500,000,000,000,000. Now, without touching a thing, the scientists boosted the known accuracy of the machine to one part in 4,300,000,000,000,000.

NPL's Krzysztof Szymaniec said the boosted accuracy is not about having international bragging rights, but better standards leads to better technology.

"Nowadays definitions for electrical units are based on accurate frequency measurements, so it's vital for the UK as an economy to maintain a set of standards, a set of procedures, that underpin technical development," he told BBC News.

"The fact that we can develop the most accurate standard has quite measurable economic implications."

The work will be published in the journal Metrologia.

Penn State University also contributed to this work.

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Image 2: A caesium fountain clock that keeps the United Kingdom's atomic time is now the most accurate long-term timekeeper in the world, according to a new evaluation of the clock that will be published in the October 2011 issue of the international scientific journal Metrologia by a team of physicists at the National Physical Laboratory (NPL) in the United Kingdom and Penn State University in the United States. This image shows the clock, NPL-CsF2, which is located at the National Physical Laboratory in Teddington, U.K. The whole device is approximately 8.2 feet (2.5 m) high. Atoms are tossed up 3.2 feet (1 m), approximately 12 inches (30 cm) above the cavity that is contained inside a vacuum vessel. The large external cylinder screens the atoms inside the clock from the relatively large and unstable external magnetic field. Credit: National Physical Laboratory, United Kingdom